Suggestion for best stereo amp ?

Sanders Magtech. 

Not much better than that. 

Budget?

I know, a lot of Americans loves Krell, Pass labs, Wilson,Magnepan,.. but the most important thing is a good and neutral position between high,mid and low. THe most if those systems give to much in low and influence mid, and a in some circumstances high to. You need a perfect balans: Audio Note,Gamut,esoteric,gryphon, soulution. And take “natural speakers,like the Ilumnia Magister. Best speaker i ever heard.

+1 Lukaske. 
Balance is key. You have to like it though. My audio note is very much balanced and natural sounding. When I put an other amp in my system that has less balance most of the time I like it more at first.  Mid range that is more pronounced is very attracting but after a while I notice that everything starts sounding the same to me. The unbalance or colorations if you can call them that way infuence every peace of music. 

I think that you can pick out “more” balanced and natural sounding amps when you listen to them side by side. It is a matter of preference and perhaps something that takes a little longer to notice. Like TV’s in a shop. The one that stands out draws your attention but if you look longer you find the one you like for the long term. 

Gryphon could be a natural upgrade choice. I would get Gryphon preamp as well. But before all that perhaps you might want to upgrade speakers as well. In other words, upgrade everything, either all at once or step by step.